libunit-wasm: Add a luw_req_buf_copy() function

This is analogous to luw_req_buf_append() but rather than appending
request data to the buffer it simply overwrites what's currently there.

This is needed to take advantage of the new ability to receive >4GiB
requests/payloads.

On a new request you would call luw_init_ctx(), luw_set_req_buf() &
open(2).

On subsequent calls to the request_handler (for this same HTTP
request/upload) you would call this new function and then write out the
data to a file.

E.g

  /* In the request_handler */
  if (total_bytes_wrote == 0) {
          luw_init_ctx(&ctx, addr, 0);
          luw_set_req_buf(&ctx, &request_buf, LUW_SRB_NONE);

          fd = open("/var/tmp/large-file.dat", O_CREAT|O_TRUNC|O_WRONLY,
                    0666);
  } else {
          luw_req_buf_copy(&ctx, addr);
  }

  buf = luw_get_http_content(&ctx);
  bytes_wrote = write(fd, buf, luw_get_http_content_sent(&ctx));
  total_bytes_wrote += bytes_wrote;
  if (total_bytes_wrote == luw_get_http_content_len(&ctx)) {
          close(fd);
          total_bytes_wrote = 0;
          luw_http_response_end();
  }

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

Author: ac000

src/c/include/unit/unit-wasm.h

@@ -238,6 +238,7 @@ extern size_t luw_get_response_data_size(const luw_ctx_t *ctx);
 extern int luw_mem_writep(luw_ctx_t *ctx, const char *fmt, ...);
 extern size_t luw_mem_writep_data(luw_ctx_t *ctx, const u8 *src, size_t size);
 extern void luw_req_buf_append(luw_ctx_t *ctx, const u8 *src);
+extern void luw_req_buf_copy(luw_ctx_t *ctx, const u8 *src);
 extern size_t luw_mem_fill_buf_from_req(luw_ctx_t *ctx, size_t from);
 extern void luw_mem_reset(luw_ctx_t *ctx);
 extern void luw_http_set_response_status(luw_http_status_t status);

src/c/libunit-wasm.c

@@ -304,6 +304,17 @@ void luw_req_buf_append(luw_ctx_t *ctx, const u8 *src)
 	ctx->req->total_content_sent = req->total_content_sent;
 }
 
+/* Copy data from the request to the previously setup request_buffer. */
+void luw_req_buf_copy(luw_ctx_t *ctx, const u8 *src)
+{
+	struct luw_req *req = (struct luw_req *)src;
+
+	memcpy(ctx->reqp + ctx->req->content_off, src + req->content_off,
+	       req->request_size);
+	ctx->req->content_sent = req->content_sent;
+	ctx->req->total_content_sent = req->total_content_sent;
+}
+
 /*
  * Convenience function to fill the response buffer with data from
  * the request buffer.